Estimation of global solar radiation using solar PV and its comparison with sunshine duration using quadratic and Gaussian fits

Abstract

Solar energy is the prime energy source of hydrologic parameter such as evapotranspiration and aerodynamic parameter like wind. Knowledge of daily global solar radiation is important to estimate all solar energy related parameters. In this study, mean daily global solar radiation at Haramaya University (HU) and Dire Dawa (DD) meteorological stations were estimated using sunshine duration data, which were recorded using Campbell-Stock Heliograph as the input of Angstrom-Prescott model. These values were further used to calculate the half hourly power intensity of solar radiation by applying Collares-Pereira and Rabl’s model. A 14 cm by 14 cm 12 V solar module was used to take indirect measurements of the solar radiation at the interval of 30 minutes from sunrise to sunset throughout the course of the study period. Readings were made in terms of voltage using a multi-meter, from which power intensities were calculated. Finally, comparisons were made between the estimated values of the half hourly power intensity of the solar radiation and the corresponding measured values to examine the degree of variability between the measured and estimated values of solar radiations using quadratic and Gaussian fits. The estimated values of the half hourly power intensity of the solar radiation agreed closely with the corresponding measured values within the error range of 15% when Gaussian fit was used but only within the error range of 10% when the quadratic fit was used. Gaussian fit reflected the actual solar radiation better than the quadratic fit despite the larger difference between the estimated and measured values. It could be concluded that satisfactory estimates of mean daily global solar radiation were obtained at both locations by using solar modules in the absence of pyranometers, and the errors could be minimized by selecting the appropriate mathematical function.

Keywords: Campbell-Stock Heliograph, Solar Module; Angstrom-Prescott model; Half hourly power intensity; Collares-Pereira; Rabl’s model